This invention relates to polyurethanes and is particularly concerned with the use of a monohydroxylated polybutadiene as a reactive plasticiser in the preparation of polyurethanes from polyisocyanates and polyols.
Polyurethanes may be prepared from polyisocyanates and polyols, for example diols such as polyether diols, polyester diols and polytetramethylene glycols. These hydroxy-terminated compounds serve to extend the chain, and possess at least two hydroxyl groups per molecule. Polyurethanes are usually plasticised by means of plasticisers whereby a softening of the polymer is brought about (U.S. Pat. No. 3,427,366).
Plasticisers such as phthalates and organic phosphates cannot be durably incorported into the polymer structure; hence they function as so-called external plasticisers. Generally several plasticisers are compounded together with a polyurethane in order to secure the desired advantages with respect to the properties of the polymer. External plasticisers can, however, migrate to the surface of the polymer, depending upon the chemical composition of the polymer and under the influence of the ambient conditions. It has been proposed to prevent this migration of plasticiser by internal plasticisation of the polymer and to build polymerisable plasticisers into the polymer molecule.
It is an object of the invention to provide a polyurethane composition which is internally plasticised so that the problems associated with migration of plasticiser are reduced or obviated.